For an organic light emitting diode (OLED), electrons need to be injected from a cathode when the OLED is working. The material of the cathode is selected from metals having low work function, such as Al, Mg, Ag, Ca and so on. These metals are relatively active and susceptible to moisture and oxygen to react therewith. Meanwhile, other organic materials in the OLED device are also susceptible to moisture and oxygen to subject to changes, such that the natures and properties of these materials deteriorate or fail, resulting in shortening working life of the device. Therefore, in order to attain the goal of prolonging the working life of the device, it is very important to encapsulate the device efficiently so as to isolate functional layers of the device from moisture, oxygen and the like in the surrounding environment.